1. Field of the Invention
The present invention relates to drive devices with a hydrostatic motor and a combined friction brake, and can be used for machine tools, mobile working appliances and the like. The present invention relates in particular to a drive device equipped with a radial piston motor according to the multi-stroke principle and a multiple plate brake.
2. Discussion of the Background
Hydrostatic motors within the meaning of the present invention comprise substantially a rotor and a stator, a mount for the rotor in the stator, an output shaft connected to the rotor and a controller for distribution of hydraulic fluid to cylindrical spaces in the rotor. These components are disposed around a geometric axis and fixed relative to each other in the direction of this axis. Radial piston motors, for which the present invention is preferably applied, also have a stroke ring as an element of the stator, a rotor disk as an element of the rotor, in which there are disposed the cylindrical spaces in substantially radial arrangement, and pistons, which are disposed movably in the cylindrical spaces and are braced via rollers against the stroke ring.
The function of friction brakes is to prevent (stopping brake) or limit (operating brake) relative rotation between rotor and stator. Friction brakes within the meaning of the present invention are, for example, multiple plate brakes with a brake-plate assembly, the output-side brake plates, which are fixed via a driver toothing such that they cannot turn relative to the rotor, and stator-side brake plates, which are fixed via a driver toothing such that they cannot turn relative to the stator. Via the elastic force of a spring-and-piston arrangement as a further element of the multiple plate brake, pressure is exerted on the brake-plate assembly comprising the output-side and stator-side brake plates such that the output-side and stator-side brake plates are pushed against one another, thus leading to activation of the multiple plate brake, or in other words to immobilization of the rotor during stoppage of the drive device or to braking of the rotor during operation of the drive device. Via a fluid pressure acting on the spring-and-piston arrangement in the sense opposite to the elastic force, the brake-plate assembly is relieved, thus releasing the multiple plate brake.
Such drive devices are the subject matter of constant development toward reduction of both the radial and axial space requirement thereof. In this connection, the geometry and/or arrangement of the friction brake has a decisive influence, apart from that of the geometry of the rotor mount, on the outside dimensions of the drive device both in radial and axial direction.
Drive devices with a hydrostatic motor and a multiple plate brake according to the features described in the foregoing are disclosed, for example, in German Laid-Open Applications DE A 19504451, DE A 4407563 and DE A 4311997.
In the drive device of German Laid-Open Application DE A 19504451, the brake plates of the multiple plate brake are disposed radially outside a bearing of the mount for the output shaft in such a way that they axially overlap at least part of the bearing. Such placement of the disk plates certainly does not require too much space for the drive device in axial direction, but needs a relatively large amount of space in radial direction in order to house the brake plates, the output-side driver toothing and the stationary driver toothing.
In the drive device known from German Laid-Open Application DE A 4407563, the brake plates of the multiple plate brake are disposed axially adjoining the casing of the hydrostatic motor; thus little space in radial direction but a considerable amount of space in axial direction is needed for placement of the brake plates and the two driver toothings.
The same observation is substantially true also for the drive device known from German Laid-Open Application DE A 4311997, and so this drive device will not be further explained at this place.
The object of the present invention is therefore to provide a drive device with a hydrostatic motor and a combined friction brake, which is characterized by a compact and simple structure with dimensions which in both axial and radial direction are small compared with those of conventional drive devices.
This object is achieved by a drive device according to the features of claim 1. According to the present invention, the brake body of the friction brake is disposed at least partly in an enclosure formed in the rotor. The placement of the brake body in the manner described in the foregoing therefore does not on the whole add to either the axial or the radial extent of the drive device. Furthermore, a drive device with compact and simple structure is achieved by such placement of the brake body.
A conventional multiple plate brake with a brake-plate assembly as the brake body is one example of a suitable friction brake. Of course, friction brakes with a disk-like brake body (disk brakes) or friction brakes with a drum-like brake body (drum brakes) are also possible if the enclosure has appropriate geometry. In principle, any brake having a brake body which can be disposed at least partly in an enclosure in the rotor and which can prevent or limit relative rotation between rotor and stator is conceivable.
The brake body can have arbitrary form. As regards placement of the brake body, the following options are available: The brake body can be disposed xe2x80x9cto floatxe2x80x9d in the enclosure and be provided with two friction faces that can be brought into frictional contact with corresponding friction faces on the rotor side and stator side. It is also possible, however, for the brake body to have one friction face and be in interlocking contact either with the stator or with the rotor, in which case the friction face of the brake body can then be brought into frictional contact with a corresponding friction face on the rotor or stator.
Further advantageous features of the drive device according to the invention are subject matter of the dependent claims.
As regards a simple and inexpensive alternative version of a drive device according to the invention, an already existing axial recess in the rotor, especially the axial recess for the output shaft, is used as the enclosure for placement of the brake body. Since such placement of the brake body does not have any influence on the other components provided in the drive device, components of conventional drive devices can be used in this case. Naturally this is also possible when the brake body is not disposed in the already present axial recess, but is placed in an enclosure formed specifically in the rotor for the brake body, thus contributing substantially to reduction of the costs for the drive device.
The brake body of the friction brake is preferably disposed between the rotor and a shank which is held such that it cannot turn relative to the stator but can be moved axially. The shank extends to the rotor and supports the brake body.
For actuation of the friction brake, the drive device can also be provided with a spring-and-piston arrangement, as is also used in conventional drive devices. Such spring-and-piston arrangements are usually housed in a brake casing fastened to the stator. The piston of the spring-and-piston arrangement is connected to the shank and forms two chambers in the casing. In one of the two chambers there is disposed a spring, which exerts on the piston a pressure in a first direction, for example in brake actuation direction. The other chamber can be filled with hydraulic fluid, by means of which there can be applied on the piston a pressure in a second direction, for example in brake release direction. Naturally it would also be possible to actuate the brake via the hydraulic fluid and to release it via the elastic force of the spring.
As already mentioned hereinabove, there can be used as friction brake a multiple plate brake, which is provided with a brake-plate assembly with at least one output-side brake plate and one stator-side brake plate. In this case there is advantageously formed in the enclosure in the rotor a driver toothing for the at least one output-side brake plate and on the shank a driver toothing for the at least one stationary brake plate. When the recess for the output shaft is used as the enclosure, naturally the already present internal toothing can be used as the driver toothing for the at least one output-side brake plate. Naturally it also would be conceivable to form the driver toothing not directly in the enclosure of the rotor or on the shank, but via further devices connected to the rotor or the shank such that they cannot turn relative thereto.
When the driver toothing is formed on the shank, the at least one brake plate seated on the driver toothing of the shank can be braced either directly on the shank or on a bush disposed on the shank.
A brake body within the meaning of the present invention is, however, also a brake body formed in one piece with the rotor and provided with a friction face which can be brought into frictional contact with a corresponding stator-side friction face. For example, there can be regarded as the brake body a surface-layer region enclosing the surface of the rotor disk and formed at the surface as a friction face, which can be brought into frictional contact with a corresponding stator-side friction face. The surface-layer region can be, for example, a coated or hardened region of the rotor-disk surface having a certain depth. The material of the rotor disk surrounding this region then corresponds to the enclosure for the region of the rotor disk regarded as the brake body.